Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

Show paginator

Hide paginator

25%

Page 1 of 4

1. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Any one of the above

Equal to unity

Always more than unity

2. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

3. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

1.33

3.33

4.33

4. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Condenser, absorber and separator (rectifier)

Evaporator

Absorber

5. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

None of the above

Maintains different temperatures in evaporator in proportion to load

6. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

1.25

5.12

7. Which of the following cycles uses air as the refrigerant?

Stirling

Ericson

Bell Coleman

Carnot

8. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

Large latent heat

Low boiling point

High risibility with oil

9. Critical temperature is the temperature above which

Water will evaporate

Water will never evaporate

A gas will never liquefy

A gas will immediately liquefy

10. The minimum temperature to which water can be cooled in a cooling tower is

Wet bulb temperature of air

Dew point temperature of air

Ambient air temperature

Dry bulb temperature of air

Page 2 of 4

11. Rating of a domestic refrigerator is of the order of

0.1 ton

10 tons

40 tons

5 tons

12. The bank of tubes at the back of domestic refrigerator is

Refrigerant cooling tubes

Capillary tubes

Evaporator tubes

Condenser tubes

13. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

None of these

Sub-cooling or under-cooling

Normal cooling

14. The freezing point of sulphur dioxide is

-56.6°C

-135.8°C

-77.7°C

-75.2°C

15. A bootstrap air cooling system has

One heat exchanger

Four heat exchangers

Two heat exchangers

Three heat exchangers

16. Which of the following statement is correct?

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

17. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.4

0.376

0.67

18. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

19. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Dry saturated vapour

Saturated liquid

Wet vapour

20. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Detect liquid in vapour

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Page 3 of 4

21. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Rankine

Carnot

Reversed Rankine

22. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 3

1: 9

9: 1

23. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

24. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Axial

Centrifugal

Piston type reciprocating

25. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

26. The boiling point of ammonia is

-33.3°C

-10.5°C

-30°C

-77.7°C

27. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

More for small capacity and less for high capacity

Less

28. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

29. Most thermostatic expansion valves are set for a superheat of

15°C

5°C

20°C

10°C

30. The capillary tube, as an expansion device, is used in

Room air conditioners

Water coolers

Domestic refrigerators

All of these

Page 4 of 4

31. For obtaining high COP, the pressure range of compressor should be

High

Any value

Optimum

Low

32. Freon group of refrigerants are

Toxic

Nontoxic and non-inflammable

Inflammable

Non-inflammable and toxic

33. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

Negative

None of these

Zero

34. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Compressor and condenser

Evaporator and compressor

Receiver and evaporator

35. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

2 bar

15 bar

30 bar

36. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Dew point temperature

Wet bulb temperature

Relative humidity

37. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Takes place at constant pressure

Takes place at constant temperature

Involves no change in volume

38. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

39. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Freon

Carbon dioxide

Ammonia

40. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Much below critical temperature

Near critical temperature of refrigerant

Above critical temperature

Share this Now with Friends:

VideRime

A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

Related

Leave a ReplyCancel reply

Ads by Google

Recent Posts

Membership Registration

Secured Payment

Protection